1. Field of the Invention
The present invention relates to an electrophotographic photoconductor drum comprising a cylindrical hollow support and a photoconductive layer provided thereon.
2. Discussion of Background
In line with the trend toward small-size, light-weight electrophotographic apparatus, there is an increasing demand for an electrophotographic photoconductor drum comprising a thin-walled support with a small diameter.
The photoconductor drum emits a noise due to the occurrence of resonance when a cleaning blade is brought into slide contact with the external surface of the photoconductor drum. In addition, the photoconductor drum also gives forth a noise in resonance with a contact type charger which is situated in contact with the photoconductor drum. Such problems of noise development have become an important research topic in recent years because the noise development is more frequent in the recent photoconductor drum which comprises a thin-walled cylindrical support with a small diameter.
It is known that the problem of noise resulting from the resonance triggered by the slide contact of the cleaning blade with the photoconductor drum is obvious when the photoconductor drum is continuously operated under the circumstance of high temperature and high humidity. Further, it is also known that the noise coming from the photoconductor drum in resonance with the contact-type charger varies depending on the frequency of an alternating voltage applied to the contact charger.
To minimize such noises, it is proposed to provide a member capable of absorbing or reducing the vibration on the inner surface of the photoconductor drum, as disclosed in Japanese Laid-Open Utility Model Application 62-127567. Japanese Laid-Open Patent Application 63-60481 describes that a cushioning member is pressed into a photoconductor drum for the same purpose as mentioned above. Further, it is proposed to fill a part of the hollow portion of the cylindrical support with a viscoelastic material as disclosed in Japanese Laid-Open Patent Application 3-105348.
The noise of the photoconductor drum in resonance with the contact charger is reduced bv setting the weight ratio of the photoconductor drum to the contact charger to 1.2 or more in Japanese Laid-Open Patent Application 5-35049; and by holding a material which is heavier than the total weight of the photoconductor drum in the hollow portion of the photoconductor drum via an elastic material such as an adhesive in Japanese Laid-Open Patent Application 5-35166. There is also the description that an elastic material such as a rubber in which a material such as finely-divided particles of metal is dispersed is inserted into the hollow portion of the photoconductor drum to curtail the noise by resonance between the contact charger and the photoconductor drum in Japanese Laid-Open Patent Application 5-188839. The weight ratio of the contact charger to the photoconductor drum is controlled to 1.0 or less in Japanese Laid-Open Patent Application 5-333668. As disclosed in Japanese Laid-Open Patent Application 6-19377, a member is inserted into the hollow portion of the photoconductor drum in such a fashion as illustrated in FIG. 3.
There is also the trend toward small-size, light-weight apparatus in the field of electrophotographic apparatus designed for producing images on an image receiving member with a large width of A3 size, A2 size, A1 size or A0 size. Therefore, a small-size, light-weight photoconductor drum is necessarily desired for the aforementioned electrophotographic apparatus.
In such electrophotographic apparatus corresponding to the image receiving member with a relatively large width, the abnormal sound also comes from the photoconductor drum when the cleaning blade is in slide contact with the external surface of the cylindrical photoconductor drum under the circumstances of high temperature and high humidity and when an alternating voltage is superposed to the contact type charger. The above-mentioned abnormal noises can be reduced to some extent by employing the previously mentioned conventional methods in combination or adjusting the conditions of such methods.
However, as the length of the cylindrical photoconductor drum increases, the abnormal noise is apt to be frequently produced from the photoconductor drum. Therefore, it becomes impossible to solve the occurrence of abnormal noise merely by the conventional methods.
Furthermore, when the cylindrical photoconductor drum with a relatively long length is subjected to electrophotographic process, another kind of noise comes from the photoconductor drum. To be more specific, this type of noise, which also results from the slide contact of the cleaning blade with the external surface of the photoconductor drum, is a squeal which is made at the action of starting and finishing the electrophotographic process. It is confirmed that such a squeal sound is produced when the speed of electrophotographic process, that is, the rotational speed of the photoconductor drum is changed. Namely, while the electrophotographic process is proceeding, the strange sound comes from the photoconductor drum when the process speed is within a specific speed range, generally in the range of as low as 80 mm/sec or less. The above-mentioned specific speed range relating to the noise development seems to vary depending upon the length and the weight of the photoconductor drum. The recent electrophotographic process is carried out at a high speed of 300 mm/sec or more, so that the electrophotographic process speed is inevitably within the above-mentioned low speed range at the initiation and termination of the electrophotographic process.
The above-mentioned problem of the squeal made at the initiation and termination of the electrophotographic process cannot be completely solved by any of the conventional methods.
Further, according to the previously mentioned conventional methods, the structure of a member which is inserted into the cylindrical hollow support is apt to be complicated. Furthermore, although there is required a thin-walled cylindrical support for the photoconductor drum in view of the curtailment of manufacturing cost and the decrease in weight of the drum, a member which is heavier than necessary is sometimes inserted into the photoconductor drum in practice. In addition, any conventional method for solving the problem of resonance noise cannot cope with the change of the configuration of the photoconductor drum, such as the change in length, thickness and diameter of the cylindrical support.
Further, there may be a risk of the cylindrical hollow support being deformed depending on the thickness of the cylindrical hollow support, the hardness of the weight-controlling member inserted into the hollow portion of the cylindrical support and method of fixing the weight-controlling member to the cylindrical support. In such a case, there is the problem that a half tone image cannot be exactly produced.